It is well known for lubricating oils to contain a number of surface active additives (including antiwear agents, dispersants, or detergents) used to protect internal combustion engines from corrosion, wear, soot deposits and acid build up. Often, such surface active additives can have harmful effects on engine component wear (in both iron and aluminium based components), bearing corrosion or fuel economy. A common antiwear additive for engine lubricating oils is zinc dialkyldithiophosphate (ZDDP). It is believed that ZDDP antiwear additives protect the engine by forming a protective film on metal surfaces. ZDDP may also have a detrimental impact on fuel economy and efficiency and copper corrosion. Consequently, engine lubricants may also contain a friction modifier to obviate the detrimental impact of ZDDP on fuel economy and corrosion inhibitors to obviate the detrimental impact of ZDDP on copper corrosion. Friction modifiers and other additives may also increase lead corrosion.
Further, engine lubricants containing phosphorus and sulphur compounds such as ZDDP have been shown to contribute in part to particulate emissions and emissions of other pollutants. In addition, sulphur and phosphorus tend to poison the catalysts used in catalytic converters, resulting in a reduction in performance of said catalysts.
There has been a commercial trend for reduction in emissions (typically reduction of NOx formation, SOx formation) and a reduction in sulphated ash in engine oil lubricants. Consequently, the amounts of phosphorus-containing antiwear agents such as ZDDP, overbased detergents such as calcium or magnesium sulphonates and phenates have been reduced. As a consequence, ashless additives have been contemplated to provide friction or antiwear performance. It is known that surface active ashless compounds such as ashless friction modifiers may in some instances increase corrosion of metal, namely, copper or lead. Copper and lead corrosion may be from bearings and other metal engine components derived from alloys using copper or lead. Consequently, there may be a need to reduce the amount of corrosion caused by ashless additives.
U.S. Pat. No. 3,790,478 discloses an aero gas turbine lubricant containing hindered ester base-stock, an alkylated dithenylamine, and an alkylated phenyl naphthylamine. The lubricant contains 0.01 wt % to 1 wt % of a C1-20 alkyl gallate as lead corrosion inhibitor (in particular propyl gallate is mentioned).
British Patent 1 358 046 discloses a lubricant 0.01 wt % to 1 wt % of a C1-20 alkyl gallate as lead corrosion inhibitor (in particular propyl gallate is mentioned).
British Patent GB 1 180389 discloses synthetic lubricating compositions useful for the lubrication of engines of jet aircraft. The lubricants contain 0.1 wt % of propyl gallate as a lead corrosion inhibitor.
British Patent GB 1 180 386 discloses an aero gas turbine lubricant. The lubricant contains 0.01 wt % to 1 wt % of a C1-20 alkyl gallate as lead corrosion inhibitor (in particular propyl gallate is mentioned with a treat rate of 0.1 wt %).
British Patent GB 1 162 818 discloses synthetic lubricants for use at very high temperatures that occur in area gas turbines. The lubricant contains 0.01 wt % to 1 wt % of a C1-20 alkyl gallate as lead corrosion inhibitor (in particular propyl gallate is mentioned with a treat rate of 0.1 wt %).
French Patent FR 2063994 discloses lubricants stabilised against aging by adding 0.2 wt % to 1 wt % of a synergistic mixture of antioxidants based on (i) an ester-substituted phenol and a pentaerythritol phosphite-propyl gallate. The pentaerythritol phosphite-propyl gallate is treated at 0.2 wt % in the examples.
French Patent FR 1 537 892 discloses synthetic lubricants for use at very high temperatures that occur in area gas turbines. The lubricant contains 0.01 wt % to 1 wt % of a C1-20 alkyl gallate as lead corrosion inhibitor (in particular propyl gallate is mentioned with a treat rate of 0.1 wt %).
U.S. Pat. No. 3,336,349 discloses alkanoyl esters of trihydroxy benzenes in lubricants to provide thermal and oxidative stability. The lubricants are useful for jet engines.
U.S. Pat. Nos. 7,423,000 and 7,582,126 disclose compositions that may contain catechol compounds such as tertiary alkyl substituted catechols.
U.S. Pat. No. 5,576,274 discloses fuel and lubricant additives useful as dispersants and multifunctional viscosity modifiers wherein a dihydroxyaromatic compound is alkylated with an olefinic polymer and then aminated in such a manner as to oxidize the hydroxyl moieties of the dihydroxyaromatic compound to carbonyl groups.
U.S. Pat. No. 2,795,548 discloses the use of lubricating oil compositions containing a borated alkyl catechol. The oil compositions are useful in the crankcase of an internal combustion engine in order to reduce oxidation of the oil and corrosion and wear of the metal parts of the engine.
U.S. Pat. No. 5,102,569 discloses a method of preparing a borated alkyl aromatic polyol. The borated alkyl aromatic polyol may be used in lubricating oil formulations to reduce oxidation, wear, and deposits in internal combustion engines.
US Patent Application 2006/019840 discloses lubricating oil for bearings, in particular, a lubricating oil for oil impregnated sintered bearings or fluid dynamic bearings. The lubricating oil may contain gallic acid-based compounds.